Unfortunately the EHA is usually what leaks. The o-rings usually aren't the problem (unless you leave them out).

I looked at the code table and 4 is for the airflow potentiometer. The device isn't sold separate from the airmeter housing. It should be tested to verify the problem. The device has a three wire connector that should have 5v, ground and the control signal. The control signal should be .5-.9v at idle and go up toward five volts.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician